The present invention relates to an apparatus and a method of feeding fluid usable in production process in the field of electronic components, household electric appliances, and the like for quantitatively discharging various fluids including adhesives, solder pastes, fluorescent substances, greases, paints, hot melts, chemicals, and foods.
Fluid dispensers have been conventionally used in various fields. With recent needs of smaller and higher memory-density electronic components, technology for controlling discharge of a micro quantity of fluid materials with high accuracy and stability is being requested.
In the case of Surface Mount Technology (SMT) for example, in the trend of mounting with higher speed, smaller size, higher density, higher grade, and increased automation, requirements for the dispenser are outlined below:
{circle around (1)} Increasing accuracy of an application quantity and minimizing an application quantity per applying operation;
{circle around (3)} Shortening discharge time, i.e., enabling interception and start of dispensation at high speed; and
{circle around (4)} Enabling dispensation of powder and granular material having high viscosity.
Conventionally for discharging a micro flow quantity of fluid, dispensers of air-pulse method, thread groove method, and micro pump method using electro- and magnetostrictive elements have come into practical use.
Among the above-described prior-art examples, widely used is the dispenser of air-pulse method as shown in FIG. 15, and the technology thereof is disclosed, for example, in “Automation Technology '93: 25th Volume No. 7”. The dispenser of this method is for applying, like a pulse, a constant quantity of air fed from a constant-pressure source into a container 200 (cylinder) and for discharging a constant quantity of fluid corresponding to a rising part of pressure in the cylinder 200 through a nozzle 201.
The dispenser of the air-pulse method has a disadvantage of poor response.
The disadvantage is attributed to compressibility of air 202 enclosed in the cylinder and to resistance of a nozzle when an air pulse is passed through a narrow space. More specifically, in the case of the air-pulse method, time constant of hydraulic circuit expressed by T=RC, that is determined by cylinder capacity: C and nozzle resistance: R, is large, and therefore after application of an input pulse, time delay of, for example, about 0.07 to 0.1 sec. should be allowed before start of discharge.
In order to solve the above disadvantage of the air-pulse method, there has been put into practical use a dispenser equipped with a needle valve on an inlet portion of a discharge nozzle for opening and closing a discharge port by moving a small-diameter spool constituting the needle valve in axis direction at high speed.
In this case, however, when fluid is intercepted, a space between members that make relative movement becomes zero, and therefore powder whose average particle size is several microns to several tens of microns is mechanically subjected to compression action and destroyed. As a result, various failures occurs, which may make it difficult to apply the dispenser to application of adhesives, conductive pastes, and fluorescent substances containing powder, and the like.
Also for the same object, a dispenser of thread groove method, that is a viscosity pump, has been already put into practice. In the case of thread grove method, it becomes possible to select pump characteristics unlikely to depend on nozzle resistance, so that in the case of continuous application, a desirable result may be obtained. However, the thread grove method is not good at intermittent application because of the characteristics of the viscosity pump. Consequently in the conventional thread groove method, following measures are taken:
(1) An electromagnetic clutch is interposed between a motor and a pump shaft, and when discharge operation is turned ON/OFF, the electromagnetic clutch is connected or released; and
(2) A DC servo motor is used to achieve quick rotation start or quick stop.
However, time constant of mechanical system determines responsibility in the both cases, which imparts restriction to high-speed intermittent operation. In terms of responsibility, the thread groove method is superior to the air-pulse method. However, the minimum time of about 0.05 sec. is a limit at best.
Further, rotation characteristics of the pump shaft at the time of transient response (at the time of rotation start and stop) have a number of uncertainty factors, so that strict control of flow quantity is difficult, and there is a limit of application accuracy.
A micro pump with use of stacked piezoelectric elements has been developed for the purpose of discharging a micro flow quantity of fluid. The micro pump is typically equipped with mechanical passive discharge valve and inlet valve.
However, it is extremely difficult for the pump composed of a spring and a ball for opening and closing the discharge valve and the inlet valve by pressure difference to perform intermittent discharge of rheological fluid having low fluidity and viscosity as high as tens of thousands to several hundred thousand centipoises with high accuracy of flow quantity and high speed (0.1 sec. or less).
In the fields of circuit formation, formation of electrodes and ribs for image tubes such as PDP and CRT, application of sealing materials for crystal liquid panels, and manufacturing process of optical disks and the like, where high accuracy and super-miniaturization are being pursued more and more in recent years, there are strong requests relating to microscopic application technology as shown below:
{circle around (1)} After continuous application, application may be quickly stopped and after a short period of time, continuous application may be started swiftly. Accordingly, it is ideal that a flow quantity may be controlled with a pitch of 0.01 sec;
{circle around (2)} Ability of discharging powder and granular material. For example, mechanical interception of a flow passage will not cause such trouble as compressive destruction of powder and clogging of the flow passage.
In order to meet various requests of recent years relating to application of a micro-flow quantity of high-viscosity fluid and powder and granular material, inventors of the present invention have filed a patent application titled “Apparatus and Method of Feeding Fluid” (patent application No. 2000-188899; unexamined patent publication No. 2002-1192) relating to an application means including the step of providing relative rectilinear motion and rotational motion to between a piston and a cylinder, providing a transportation means of fluid by the rotational motion, changing a relative gap between the fixed side and thus rotating side with use of the rectilinear motion, and thereby controlling a discharge quantity of fluid.
The present invention is a modification of the above proposal, and an object thereof is to provide a method and apparatus of applying fluid capable of increasing application accuracy with use of characteristics of each of intermittent application and continuous application by, for example, making intermittent application pseudo-continuous application or by switching intermittent application and continuous application in each step of fluid application process.